Tim;
Not sure on the MkV stuff, but the MkIV (and most cars) *do* have a high-beam flash, and it is typically activated by pulling the left stalk towards the driver. The high-beams will light up for as long as you hold the stalk in the forward position. I use this feature all the time to notify oncoming drivers at night that their high-beams are on and blinding oncoming traffic, and also to notify transports and buses that they have passed me and can safely merge back into the right lane. However, this is not at all related to the mod being discussed here!!!!
When activating the turn signal to change lanes, you can move the stalk up (right blinker) or down (left blinker) to a half-way point that will activate the blinker for as long as you hold the stalk at that half-way point. This is commonly referred to as the "lane changer position" or "lane changer feature". If you move the stalk all the way up or all the way down to it's clicked position, the blinker may not cancel itself after a lane change, since the steering wheel has not moved through enough of a rotation.
What the mod discussed here does, is add a fixed 3 blinks to the lane changer feature. Going to the half-way point and releasing will cause the blinker to blink 3 times on whichever side you indicated - you will not have to hold the stalk at the half-way point for those extra seconds while making the lane change. You can choose to still hold the stalk at the half-way point if you want more than 3 blinks.
It would be nice if you could "program" the number of blinks... I'd probably prefer 4, or even 5, in most situations.
There should be plenty of room behind the dash, above the radio, for the additional harness. Removing the hazard switch is easy - a thin knife under the edge of the side to gently pry it out, or removing the switches beside the hazard in the same fashion (rear defog, seat heater) will let you reach behind and push the hazard switch out.